Base station apparatus, mobile terminal apparatus and communication control method

ABSTRACT

A base station apparatus capable of transmitting a downlink transmission frame at transmission timing different from another base station apparatus is provided. The base station apparatus includes a blank resource setting section that sets, as a blank resource, a resource corresponding to a downlink control channel included in a downlink transmission frame transmitted from the other base station apparatus, a user data assigning section that assigns user data to the downlink transmission frame while avoiding the blank resource, and a transmission section that transmits the downlink transmission frame assigned the user data to a mobile terminal apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of and, thereby,claims benefit under 35 U.S.C. §120 to U.S. patent application Ser. No.14/858,730 filed on Sep. 18, 2015, titled, “BASE STATION APPARATUS,MOBILE TERMINAL APPARATUS AND COMMUNICATION CONTROL METHOD,” which is adivisional application of and, thereby, claims benefit under 35 U.S.C.§120 to U.S. patent application Ser. No. 13/261,460 filed on Oct. 4,2012, titled, “BASE STATION APPARATUS, MOBILE TERMINAL APPARATUS ANDCOMMUNICATION CONTROL METHOD,” which is a national stage application ofPCT Application No. PCT/JP2011/058609, filed on Apr. 5, 2011, whichclaims priority to Japanese Patent Application No. 2010-087389 filed onApr. 5, 2010. The contents of the priority applications are incorporatedby reference in their entirety.

TECHNICAL FIELD

The present invention relates to abase station apparatus, mobileterminal apparatus and communication control method in thenext-generation mobile communication system.

BACKGROUND ART

In UMTS (Universal Mobile Telecommunications System) networks, for thepurpose of improving spectral usage efficiency and further improvingdata rates, by adopting HSDPA (High Speed Downlink Packet Access) andHSUPA (High Speed Uplink Packet Access), it is performed exploitingmaximum features of the system based on W-CDMA (Wideband Code DivisionMultiple Access). For the UMTS network, for the purpose of furtherincreasing high-speed data rates, providing low delay and the like, LongTerm Evolution (LTE) has been studied (Non-patent Literature 1). In LTE,as a multiplexing scheme, OFDMA (Orthogonal Frequency Division MultipleAccess) different from W-CDMA is used in downlink, while SC-FDMA (SingleCarrier Frequency Division Multiple Access) is used in uplink.

In the 3G system, a fixed band of 5 MHz is substantially used, and it ispossible to achieve transmission rates of approximately maximum 2 Mbpsin downlink. Meanwhile, in the LTE system, using variable bands rangingfrom 1.4 MHz to 20 MHz, it is possible to achieve transmission rates ofmaximum 300 Mbps in downlink and about 75 Mbps in uplink. Further, inthe UMTS network, for the purpose of further increasing the wide-bandand high speed, successor systems to LTE have been studied (for example,LTE Advanced (LTE-A)). In LTE-A (LTE Release 10), a Heterogeneousnetwork configuration is studied in which importance is attached to alocal area environment in addition to conventional cellularenvironments.

CITATION LIST Non-Patent Literature

Non-Patent Literature 1: 3GPP, TR25.912 (V7.1.0), “Feasibility Study forEvolved UTRA and UTRAN”, September 2006

SUMMARY OF THE INVENTION Technical Problem

The present invention was made in view of such a respect, and it is anobject of the invention to provide a base station apparatus, mobileterminal apparatus and communication control method for enabling controladapted to interference inside a Heterogeneous network to be performedto support the next-generation mobile communication system.

Solution to Problem

A base station apparatus of the invention is a base station apparatuswhich shares at least a part of a frequency band with another basestation apparatus that covers a large-scale cell, covers a small-scalecell, and is capable of transmitting a downlink transmission frame attransmission timing different from the another base station apparatus,and is characterized by having a blank resource setting sectionconfigured to set resources, in which the downlink transmission frameundergoes interference from another downlink transmission frameincluding a blank period transmitted from the another base stationapparatus, as blank resources, a user data assigning section configuredto assign user data to the downlink transmission frame while avoidingthe blank resources, and a transmission section configured to transmitthe downlink transmission frame assigned the user data to a mobileterminal apparatus.

A base station apparatus of the invention is a base station apparatuswhich shares at least a part of a frequency band with another basestation apparatus that covers a small-scale cell, covers a large-scalecell, and is capable of transmitting a downlink transmission frame attransmission timing different from the another base station apparatus,and is characterized by having a blank resource setting sectionconfigured to set resources, in which the downlink transmission frameinterferes with a downlink control channel of another downlinktransmission frame transmitted from the another base station apparatus,as blank resources, a user data assigning section configured to assignuser data to the downlink transmission frame while avoiding the blankresources, and a transmission section configured to transmit thedownlink transmission frame assigned the user data to a mobile terminalapparatus.

Technical Advantages of the Invention

According to the invention, interference is suppressed which is imposedon a downlink transmission frame transmitted from a base stationapparatus of a small-scale cell by a downlink transmission frametransmitted from a base station apparatus of a large-scale cell. Thus,it is possible to cause the base station apparatus of the large-scalecell and the base station apparatus of the small-scale to performcontrol adapted to interference inside a Heterogeneous network havingthe large-scale cell and the small-scale cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view of a system band of an LTE system;

FIG. 2 is an explanatory view of the outline of a Heterogeneous network;

FIG. 3 is an explanatory view of interference of radio frames of amacro-cell and a pico-cell;

FIG. 4 is an explanatory view of an interference suppression method forradio frames of the micro-cell and the pico-cell;

FIG. 5 is an explanatory view showing an example of transmission controlprocessing in a base station apparatus of the pico-cell;

FIG. 6 is an explanatory view of transmission control processing in abase station apparatus of the macro-cell;

FIG. 7 is an explanatory view of a configuration of a radiocommunication system;

FIG. 8 is an explanatory view of the entire configuration of the basestation apparatus;

FIG. 9 is an explanatory view of the entire configuration of a mobileterminal apparatus;

FIG. 10 is a conceptual diagram of a process of generating a downlinktransmission frame in the base station apparatus of the pico-cell;

FIG. 11 is a conceptual diagram of a process of receiving the downlinktransmission frame in the mobile terminal apparatus that communicatesvia the pico-cell;

FIG. 12 is a conceptual diagram of a process of generating a downlinktransmission frame in the base station apparatus of the macro-cell; and

FIG. 13 is a conceptual diagram of a process of receiving the downlinktransmission frame in the mobile terminal apparatus that communicatesvia the macro-cell.

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a diagram to explain a frequency usage state when mobilecommunications are performed in downlink. In addition, in the followingdescriptions, a base frequency block is described as a componentcarrier. The example as shown in FIG. 1 is of the frequency usage statein the case of coexistence of LTE-A systems that are first mobilecommunication systems having first relatively wide system bandscomprised of a plurality of component carriers, and LTE systems that aresecond mobile communication systems having a second relatively narrowsystem band (herein, comprised of a single component carrier). In theLTE-A systems, for example, radio communications are performed with avariable system bandwidth of 100 MHz or less, and in the LTE systems,radio communications are performed with a variable system bandwidth of20 MHz or less. The system band of the LTE-A system is at least one basefrequency region (component carrier: CC) with a system band of the LTEsystem as a unit. Thus integrating a plurality of base frequency regionsto broaden the band is referred to as carrier aggregation.

For example, in FIG. 1, the system band of the LTE-A system is a systemband (20 MHz×5=100 MHz) containing bands of five component carrierswhere the system band (base band: 20 MHz) of the LTE system is onecomponent carrier. In FIG. 1, a mobile terminal apparatus UE (UserEquipment) #1 is a mobile terminal apparatus supporting the LTE-A system(also supporting the LTE system), and has the system band of 100 MHz,UE#2 is a mobile terminal apparatus supporting the LTE-A system (alsosupporting the LTE system), and has the system band of 40 MHz (20MHz×2=40 MHz), and UE#3 is a mobile terminal apparatus supporting theLTE system (not supporting the LTE-A system), and has the system band of20 MHz (base band).

In addition, in the LTE-A system, a Heterogeneous network (hereinafter,referred to as HetNet) configuration is studied in which importance isattached to a local area environment. As shown in FIG. 2, the HetNet isa hierarchical network for overlaying various forms of cells of apico-cell C1, femto-cell and the like (small-scale cells) in addition toa conventional macro-cell C2 (large-scale cell). In the HetNet, a basestation apparatus B2 of the macro-cell C2 for covering a relativelylarge area is set for downlink transmission power higher than a basestation apparatus B1 of the pico-cell C1 for covering a relativelynarrow area.

Accordingly, when the macro-cell C2 and the pico-cell C1 are operatedwith close frequency bands, as shown in FIG. 3, there is a problem thata radio frame from the base station apparatus B1 of the pico-cell C1undergoes large interference from a radio frame from the base stationapparatus B2 of the macro-cell C2. Therefore, in the pico-cell C1,coverage is narrowed by large interference from the macro-cell C2.

Further, particularly a downlink control channel (PDCCH: PhysicalDownlink Control Channel) arranged at the beginning of a subframe isbasically not retransmitted as distinct from a downlink data channel(PDSCH: Physical Downlink Shared Channel), and therefore, is given asignificant effect by interference from the macro-cell C2. Furthermore,a broadcast channel (PBCH: Physical Broadcast Channel) shown by B in thesubframe and cell-search synchronization signal (PSS: PrimarySynchronization Signal, SSS: Secondary Synchronization Signal) are alsonot basically retransmitted, and therefore, are given a significanteffect by interference from the macro-cell C2.

To solve the problems, as shown in FIG. 4, considered is a method ofusing an MBSFN (Multimedia Broadcast multicast service Single FrequencyNetwork) subframe and subframe shift. The MBSFN frame is specified inthe LTE system, and is a subframe for enabling signals except a controlchannel to be a blank interval (blank period). According to thisconfiguration, overlap of downlink control channels is canceled by radioframes of the macro-cell C2 and the pico-cell C1 being shifted in thetime-axis direction. Further, the radio frame of the macro-cell C2 ispartially provided with the blank periods by the MBSFN subframes, andsuppresses interference to the downlink control channels, broadcastchannels and synchronization signals of the subframes enclosed by dashedlines of the pico-cell C1. As a result, coverage of the downlink controlchannel, broadcast channel and synchronization signal of the pico-cellC1 is ensured. Further, interference is also reduced to downlink datachannels of the subframes enclosed by dashed lines of the pico-cell C1by the blank periods of the radio frame of the macro-cell C2, andimprovements in the data rate are expected.

However, in the aforementioned method, although interference to thedownlink control channels is suppressed in the subframes of thepico-cell C1 enclosed by dashed lines, there is a problem that a part ofuser data undergoes interference from the radio frame of the macro-cellC2. Further, control channels of subframes that are not enclosed bydashed lines of the pico-cell C1 are affected by interference of theradio frame of the macro-cell C2.

Therefore, to solve the problem, the inventors of the invention arrivedat the invention. In other words, it is the gist of the invention that abase station apparatus of a pico-cell assigns user data to a subframewhile avoiding resources that undergo interference from a macro-cell,and that a base station apparatus of the macro-cell assigns user data toa subframe while avoiding resources that interfere with a controlchannel of the pico-cell.

An Embodiment of the invention will specifically be described below withreference to accompanying drawings. Referring to FIG. 5, described issuppression of interference to a downlink radio frame of the pico-cellby transmission control in a base station apparatus of the pico-cell.FIG. 5 is an explanatory view showing an example of transmission controlprocessing in the base station apparatus of the pico-cell according tothis Embodiment of the invention.

As shown in FIG. 5, a downlink radio frame of the macro-cell C2 iscomprised of 10 subframes of subframes #0 to #9, and a control channel(PDCCH) is multiplexed into OFDM symbols on the beginning side of eachsubframe. Further, the downlink radio frame of the macro-cell C2 has theabove-mentioned MBSFN subframes, and blank periods are set exceptcontrol channels of subframes except subframes #0, #4, #5 and #9. Thebroadcast channel (PBCH) and synchronization signals (PSS, SSS) for cellsearch are multiplexed into subframes #0 to #5.

Meanwhile, a downlink radio frame of the pico-cell C1 has the same radioframe configuration as the downlink radio frame of the macro-cell C2,but the subframe is not set for the blank period. Further, the downlinkradio frame of the pico-cell C1 is subframe-shifted in the time-axisdirection relatively to the radio frame of the macro-cell C2. By thismeans, a part of control channels, broadcast channels, synchronizationsignals and the like in the downlink radio frame of the pico-cell C1 arecoincident with the blank periods of the downlink radio frame of themacro-cell C2, and interference from the macro-cell C2 is suppressed. Inthe downlink radio frame of the pico-cell C1, subframes withinterference to the control channel and the like suppressed are used.

As described above, the blank periods of the downlink radio frame of themacro-cell C2 are set except the downlink control channels. Further, thesubframe of the pico-cell C1 is shifted in the time-axis direction withrespect to the MBSFN subframe of the macro-cell C2. Therefore, in thesubframe of the pico-cell C1, although interference to the controlchannel is suppressed by the blank period of the MBSFN subframe of themacro-cell C2, the data channel partially undergoes interference. Forexample, interference to the control channel is suppressed in thesubframe #6 of the pico-cell C1, but the subframe #6 undergoesinterference from the subframe #9 of the macro-cell C2. Further, thesubframes #4 and #5 of the pico-cell C1 undergo interferencerespectively by downlink control channels of the subframes #7 and #8 ofthe macro-cell C2. In this Embodiment, the base station apparatus 20(see FIG. 7) of the pico-cell C1 transmits the downlink radio frame to amobile terminal apparatus 10 while avoiding resources that undergointerference from the downlink radio frame of the macro-cell C2.

In other words, in the downlink radio frame of the pico-cell C1,resources that undergo interference from the downlink radio frame of themacro-cell C2 are set as blank resources, and user data is assignedexcept the blank resources. The user data is assigned to each mobileterminal apparatus on a resource block basis in each subframe by ascheduler. One resource block is comprised of 12 contiguous subcarriers,and is configured with a resource element as a minimum unit. In theresource block, first 3 symbols are used for the downlink controlchannel, and downlink reference signals for each transmission antennaare arranged in a part thereof. Accordingly, in the resource block ofthe pico-cell C1, the user data is assigned to resource elements thatavoid the downlink control channel, downlink reference signals and blankresources. For example, in the subframe #4 of the pico-cell C1, the 5thto 7th symbols undergo interference by the control channel of thesubframe #7 of the macro-cell C2. Therefore, in the subframe #4 of thepico-cell C1, the user data is assigned to resource elements in theregions that avoid the 1st to 3rd symbols, 5th to 7th symbols, downlinkreference signals, and the like.

The blank resources of the downlink radio frame of the pico-cell C1 areset based on the shift amount of transmission timing of downlink radioframes of the pico-cell C1 and the macro-cell C2, and a set position ofthe blank period of the downlink radio frame of the macro-cell C2. Theshift amount indicates a shift of the downlink control channel in eachsubframe of the pico-cell C1 and the macro-cell C2. Therefore, in thesubframe of the pico-cell C1, resources undergoing interference from thedownlink control channel of the macro-cell C2 are specified by the shiftamount. The set position of the blank period enables a subframe with nointerference to the control channel of the pico-cell C1 to be specifiedby combining with the shift amount. In this case, in the subframe of thepico-cell C1, as in the subframe #6, in the subframe with nointerference to the control channel, resources undergoing interferencefrom the downlink control channel and the downlink data channel of themacro-cell C2 are specified. Thus, resources undergoing interferencefrom the downlink radio frame of the macro-cell C2 are specified, andthe resources are set as blank resources.

In addition, the blank resources set by the base station apparatus ofthe pico-cell are resources set on the premise of undergoinginterference from the radio frame of the micro-cell C2. In this case,the blank resources may be resources to which any data is not assignedat all, or may be defined as resources to which unnecessary data isassigned. Further, the blank resources may be defined as resourcestransmitted with transmission power of predetermined transmission poweror less.

In addition, the shift amount may be configured so that the base stationapparatus 20 of the pico-cell C1 (see FIG. 7) receives signaling of thebase station apparatus 40 of the macro-cell, alternatively, the reversemay be possible. Further, the base station apparatus 40 of themacro-cell notifies the base station apparatus 20 of the pico-cell ofthe set position of the blank period. In addition, in the case ofsuppressing only interference by the control channel of the macro-cellC2, the base station apparatus 40 of the macro-cell does not need tonotify the base station apparatus 20 of the pico-cell of the setposition of the blank period.

Further, the mobile terminal apparatus 10 of the pico-cell C1 isnotified of the allocation position of the blank resources of thedownlink radio frame of the pico-cell C1 as blank resource information.By this configuration, the mobile terminal apparatus 10 of the pico-cellC1 is capable of demodulating the user data while avoiding the blankresources of the downlink radio frame. In this case, the blank resourceinformation may be notified to the mobile terminal apparatus 10 for eachsubframe. Further, when the blank resource information is stored in themobile terminal apparatus 10 in association with the shift amount oftransmission timing of downlink radio frames of the pico-cell C1 and themacro-cell C2, notification to the mobile terminal apparatus 10 is notnecessary. This is because the mobile terminal apparatus 10 is capableof estimating the allocation position of the blank resources from theshift amount. By this configuration, the base station apparatus 20 ofthe pico-cell C1 notifies the mobile terminal apparatus 10 of only theshift amount, and it is possible to reduce overhead.

Described next is suppression of interference to downlink controlchannels of a downlink radio frame of the pico-cell by transmissioncontrol in the base station apparatus of the macro-cell. FIG. 6 is anexplanatory view showing an example of transmission control processingin the base station apparatus of the macro-cell according to thisEmbodiment of the invention.

In the above-mentioned transmission control in the pico-cell C1,interference is suppressed only to a part of control channels by theblank periods of the downlink radio frame of the macro-cell C2.Therefore, in the pico-cell C1, used is a part of subframes withinterference to control channels suppressed. In this Embodiment, thebase station apparatus 40 of the macro-cell C2 transmits a downlinkradio frame to a mobile terminal apparatus 30 while avoiding resourcesthat interfere with control channels of a downlink radio frame of thepico-cell C1.

In other words, in the downlink radio frame of the macro-cell C2,resources that interfere with downlink control channels of the downlinkradio frame of the pico-cell C1 are set as blank resources, and userdata is assigned to resources except the blank resources. Accordingly,the user data is assigned to resource elements that avoid the downlinkcontrol channel, downlink reference signals, and blank resources thatinterfere with downlink control channels of the pico-cell in thesubframe of the macro-cell C2. For example, in the subframe #4 of themacro-cell C2, the 5th to 7th symbols interfere with the control channelof the subframe #2 of the pico-cell C1. Therefore, in the subframe #4 ofthe macro-cell C2, the user data is assigned to resource elements inregions that avoid the 1st to 3rd symbols, 5th to 7th symbols, downlinkreference signals and the like.

The blank resources of the downlink radio frame of the macro-cell C2 areset based on the shift amount of transmission timing of downlink radioframes of the pico-cell C1 and the macro-cell C2. The shift amountindicates a shift of the downlink control channel in each subframe ofthe pico-cell C1 and the macro-cell C2. Therefore, in the subframe ofthe macro-cell C2, resources that interfere with the downlink controlchannel of the pico-cell C1 are specified by the shift amount. Thus,resources that interfere with the downlink radio frame of the pico-cellC1 are specified, and the resources are set as blank resources. Inaddition, the shift amount may be configured so that the base stationapparatus 40 of the macro-cell C2 (see FIG. 7) receives signaling of thebase station apparatus 20 of the pico-cell, alternatively, the reversemay be possible.

In addition, the blank resources set in the base station apparatus ofthe macro-cell are resources set not to interfere with the controlchannel of the radio frame of the pico-cell C1. In this case, the blankresources may be resources to which any data is not assigned at all, ormay be defined as resources to which unnecessary data is assigned.Further, the blank resources may be defined as resources transmittedwith transmission power of predetermined transmission power or less.

Further, the mobile terminal apparatus 30 of the macro-cell C2 isnotified of the allocation position of the blank resources of thedownlink radio frame of the macro-cell C2 as blank resource information.By this configuration, the mobile terminal apparatus 30 of themacro-cell C2 is capable of demodulating the user data while avoidingthe blank resources of the downlink radio frame. In this case, the blankresource information may be notified to the mobile terminal apparatus 30for each subframe. Further, when the blank resource information isstored in the mobile terminal apparatus 30 in association with the shiftamount of transmission timing of downlink radio frames of the pico-cellC1 and the macro-cell C2, notification to the mobile terminal apparatus30 is not necessary. This is because the mobile terminal apparatus 30 iscapable of estimating the allocation position of the blank resourcesfrom the shift amount. By this configuration, the base station apparatus40 of the macro-cell C2 notifies the mobile terminal apparatus 30 ofonly the shift amount, and it is possible to reduce overhead.

Herein, a radio communication system according to the Embodiment of theinvention will be described specifically. FIG. 7 is an explanatory viewof a system configuration of the radio communication system according tothis Embodiment. In addition, for example, the radio communicationsystem as shown in FIG. 7 is a system including the LTE system, or SUPER3G. Further, the radio communication system may be called IMT-Advancedor may be called 4G.

As shown in FIG. 7, the radio communication system is the HetNet, and ahierarchical network is constructed using the first system having themacro-cell C2 and the second system having the pico-cell C1. The firstsystem includes the base station apparatus 40 that covers the macro-cellC2, and mobile terminal apparatuses 30 (only one is shown) thatcommunicate with the base station apparatus 40 and is comprised thereof.The second system includes the base station apparatus 20 that covers thepico-cell C1, and mobile terminal apparatuses 10 (only one is shown)that communicate with the base station apparatus 20 and is comprisedthereof. In the base station apparatuses 20, 40, each schedulerallocates radio resources on a resource block basis for each user.Further, each of the base station apparatuses 20, 40 is connected to anupper station apparatus, not shown, and is connected to a core network50 via the upper station apparatus. In addition, for convenience indescription, the description is given while assuming that equipmentsthat perform radio communication with the base station apparatuses 20,40 are mobile terminal apparatuses, and more generally, the equipmentsmay be user equipments (UEs) including mobile terminal apparatuses andfixed terminal apparatuses.

In the radio communication system, as a radio access scheme, OFDMA(Orthogonal Frequency Division Multiple Access) is applied in downlink,while SC-FDMA (Single-Carrier Frequency Division Multiple Access) isapplied in uplink. OFDMA is a multicarrier transmission scheme fordividing a frequency band into a plurality of narrow frequency bands(subcarriers), and mapping data to each subcarrier to performcommunication. SC-FDMA is a single-carrier transmission scheme fordividing the system band into bands comprised of a single or consecutiveresource blocks for each terminal so that a plurality of terminals usesmutually different bands, and thereby reducing interference among theterminals.

Described herein are communication channels in the LTE system.Communication channels in downlink have the PDSCH as a downlink datachannel shared among mobile terminal apparatuses, and downlink L1/L2control channels (PDCCH, PCFICH, PHICH). User data and higher controlinformation is transmitted on the PDSCH. Scheduling information of thePDSCH and PUSCH and others are transmitted on the PDCCH. The number ofOFDM symbols used in the PDCCH is transmitted on the PCFICH (PhysicalControl Format

Indicator Channel). ACK/NACK of HARQ (Hybrid Automatic Repeat reQuest)to the PUSCH is transmitted on the PHICH (Physical Hybrid-ARQ IndicatorChannel).

Uplink communication channels have the PUSCH (Physical Uplink SharedChannel) as an uplink data channel shared among mobile terminalapparatuses, and the PUCCH (Physical Uplink Control Channel) that is anuplink control channel. User data and higher control information istransmitted on the PUSCH. Further, downlink radio quality information(CQI: Channel Quality Indicator), ACK/NACK and others are transmitted onthe PUCCH.

Referring to FIG. 8, described next is the entire configuration of thebase station apparatus that covers the pico-cell according to thisEmbodiment. In addition, the base station apparatus that covers themacro-cell has the same configuration as that of the base stationapparatus of the pico-cell, and the description thereof is omittedherein. Further, for convenience in description, the processing ofsignals transmitted from the mobile terminal apparatus to the basestation apparatus in uplink is omitted.

The base station apparatus 20 is provided with a transmission/receptionantenna 201, amplifying section 202, transmission/reception section 203,baseband signal processing section 204, call processing section 205 andtransmission path interface 206. The user data transmitted from the basestation apparatus 20 to the mobile terminal apparatus 10 in downlink isinput to the baseband signal processing section 204 via the transmissionpath interface 206 from the upper station apparatus.

The baseband signal processing section 204 performs, on a signal of thedownlink data channel, PDCP layer processing, segmentation andconcatenation of the user data, RLC (Radio Link Control) layertransmission processing such as transmission processing of RLCretransmission control, MAC (Medium Access Control) retransmissioncontrol e.g. transmission processing of HARQ, scheduling, transmissionformat selection, channel coding, Inverse Fast Fourier Transform (IFFT)processing and precoding processing. Further, with respect to a signalof the downlink control channel, the transmission processing such aschannel coding and Inverse Fast Fourier Transform is also performed.Furthermore, on the broadcast channel, the baseband signal processingsection 204 notifies the mobile terminal apparatuses 10 connected to thesame cell C1 of control information for each mobile terminal apparatus10 to perform radio communication with the base station apparatus 20.

The transmission/reception section 203 converts the frequency of thebaseband signal output from the baseband signal processing section 204into a radio frequency band. The amplifying section 202 amplifies thetransmission signal with the frequency converted to output to thetransmission/reception antenna 201.

Referring to FIG. 9, described next is the entire configuration of themobile terminal apparatus located in the pico-cell according to this

Embodiment. In addition, the mobile terminal apparatus located in themacro-cell has the same configuration as that of the mobile terminalapparatus located in the pico-cell, and the description thereof isomitted herein. Further, for convenience in description, the processingof signals transmitted from the mobile terminal apparatus to the basestation apparatus in uplink is omitted.

The mobile terminal apparatus 10 is provided with atransmission/reception antenna 101, amplifying section 102,transmission/reception section 103, baseband signal processing section104 and application section 105. With respect to transmission data indownlink, a radio frequency signal received in thetransmission/reception antenna 101 is amplified in the amplifyingsection 102, subjected to frequency conversion in thetransmission/reception section 103, and is converted into a basebandsignal.

The baseband signal processing section 104 performs, on the basebandsignal, FFT processing, error correcting decoding, reception processingof retransmission control, etc. Among the data in downlink, user data indownlink is transferred to the application section 105. The applicationsection 105 performs processing concerning layers higher than thephysical layer and MAC layer and the like. Further, among the data indownlink, broadcast information is also transferred to the applicationsection 105.

Referring to FIG. 10, described is a process of generating a downlinktransmission frame in the base station apparatus that covers thepico-cell. FIG. 10 is a conceptual diagram of the process of generatinga downlink transmission frame in the base station apparatus that coversthe pico-cell according to this Embodiment.

As shown in FIG. 10, the process of generating a transmission frame hasa blank resource position determining section 211 and a transmissionframe generating section 212. The blank resource position determiningsection 211 determines an allocation position of blank resources, basedon the set position of the blank period notified from the base stationapparatus 40 of the macro-cell C2 and the shift amount as describedabove. In this case, the blank resource position determining section 211identifies a subframe of which the downlink control channel does notundergo interference by the shift amount and the set position of theblank period. Further, in the subframe, the blank resource positiondetermining section 211 identifies the resource position that undergoesinterference from the downlink control channel and downlink data channelof the downlink transmission frame of the macro-cell C2, and determinesthe allocation position of blank resources. Thus, resources in which thedownlink transmission frame of the macro-cell C2 undergoes interferenceare set as blank resources.

Next, the transmission frame generating section 212 arranges user datawhile avoiding downlink control channels, downlink reference signals,blank resources, etc. based on the allocation position of the blankresources, and applies the other transmission processing to generate adownlink transmission frame.

Referring to FIG. 11, described is a process of receiving the downlinktransmission frame in the mobile terminal apparatus that communicatesvia the pico-cell. FIG. 11 is a conceptual diagram of the process ofreceiving the downlink transmission frame in the mobile terminalapparatus that communicates via the pico-cell according to thisEmbodiment.

As shown in FIG. 11, the process of receiving the transmission frame hasa blank resource information acquiring section 111, and a user datademodulation section 112. The blank resource information acquiringsection 111 acquires the blank resource information indicative of theallocation position of the blank resources from the base stationapparatus 20. The blank resource information may be information thatdirectly indicates the allocation position of the blank resources, ormay be the shift amount of downlink radio frames of the pico-cell C1 andthe macro-cell C2 as described above. Further, the mobile terminalapparatus 10 may acquire the blank resource information for eachsubframe.

The user data demodulation section 112 demodulates the user data fromthe transmission frame based on the blank resource information. In thiscase, the user data demodulation section 112 demodulates the user data,while ignoring resources indicated by the blank resource information.

Thus, the base station apparatus 20 of the pico-cell C1 assigns the userdata to subframes while avoiding resources that undergo interferencefrom the downlink radio frame of the macro-cell C2. Therefore, in thedownlink transmission frame of the pico-cell C1, interference todownlink data channels is suppressed in subframes with interference todownlink control channels from the macro-cell C2 suppressed.

Referring to FIG. 12, described is a process of generating a downlinktransmission frame in the base station apparatus that covers themacro-cell. FIG. 12 is a conceptual diagram of the process of generatinga downlink transmission frame in the base station apparatus that coversthe macro-cell according to this Embodiment.

As shown in FIG. 12, the process of generating a transmission frame hasa blank resource position determining section 411 and a transmissionframe generating section 412. The blank resource position determiningsection 411 determines an allocation position of blank resources, basedon the shift amount of radio frames in the macro-cell C2 and thepico-cell C1. In this case, the blank resource position determiningsection 411 identifies a resource position that interferes with thedownlink control channel of the downlink radio frame of the pico-cell C1by the shift amount, and determines the allocation position of blankresources. Thus, resources that interfere with the control channel ofthe transmission frame of the pico-cell C1 are set as blank resources.

Next, the transmission frame generating section 412 arranges user datawhile avoiding downlink control channels, downlink reference signals,blank resources, etc. based on the allocation position of the blankresources, and applies the other transmission processing to generate adownlink transmission frame.

Referring to FIG. 13, described is a process of receiving the downlinktransmission frame in the mobile terminal apparatus that communicatesvia the macro-cell. FIG. 13 is a conceptual diagram of the process ofreceiving the downlink transmission frame in the mobile terminalapparatus that communicates via the macro-cell according to thisEmbodiment.

As shown in FIG. 13, the process of receiving the transmission frame hasa blank resource information acquiring section 311, and a user datademodulation section 312. The blank resource information acquiringsection 311 acquires the blank resource information indicative of theallocation position of the blank resources from the base stationapparatus 40. The blank resource information may be information thatdirectly indicates the allocation position of the blank resources, ormay be the shift amount of downlink radio frames of the pico-cell C1 andthe macro-cell C2 as described above. Further, the mobile terminalapparatus 30 may acquire the blank resource information for eachsubframe.

The user data demodulation section 312 demodulates the user data fromthe transmission frame based on the blank resource information. In thiscase, the user data demodulation section 312 demodulates the user data,while ignoring resources indicated by the blank resource information.

Thus, the base station apparatus 40 of the macro-cell C2 assigns theuser data to subframes while avoiding resources that interfere with thecontrol channel of the downlink radio frame of the pico-cell C1.Therefore, in the downlink transmission frame of the pico-cell C1,interference to the downlink control channel from the macro-cell C2 issuppressed.

As described above, according to the base station apparatuses 20, 40according to this Embodiment, interference is suppressed which adownlink transmission frame transmitted from the base station apparatusof the pico-cell undergoes from a downlink transmission frametransmitted from the base station apparatus of the macro-cell. In otherwords, interference of data channels is suppressed in subframes withinterference of control channels of the pico-cell C1 suppressed by MBSFNsubframes of the downlink transmission frame of the macro-cell C2.Further, in subframes except the MBSFN subframes of the downlinktransmission frame of the macro-cell C2, interference to controlchannels of the downlink transmission frame of the pico-cell issuppressed. Accordingly, interference to the downlink transmission frameof the pico-cell is sufficiently suppressed. Thus, it is possible tocause the base station apparatuses 20, 40 to perform control adapted tointerference inside the Heterogeneous network having the macro-cell C2and the pico-cell C1.

In addition, the aforementioned Embodiment describes the base stationapparatus that covers the pico-cell as a small-scale cell, but theinvention is not limited to this configuration. It is essential onlythat the base station apparatus covers a cell that undergoesinterference from the macro-cell, and the base station apparatus may besmall-sized base station apparatuses that cover a femto-cell, micro-celland the like.

Further, in the above-mentioned Embodiment, the blank period indicates aperiod during which the radio frame of the pico-cell is not affected byinterference from the radio frame of the macro-cell. In the radio frameof the macro-cell, the blank period may be a period during which no datais transmitted, or may be defined as a period during which data istransmitted to the extent that does not affect interference. Further, inthe radio frame of the macro-cell, the blank period may be defined as aperiod during which transmission is performed with transmission power ofthe extent that does not have any effect of interference on the radioframe of the pico-cell. Furthermore, in the radio frame of themacro-cell, the blank period may be defined as a period during whichtransmission is performed with an interfering amount of the extent thatdoes not affect the radio frame of the pico-cell.

The present invention is not limited to the above-mentioned Embodiment,and is capable of being carried into practice with various modificationsthereof. For example, without departing from the scope of the invention,assignment of component carriers, the number of processing sections,processing procedures, the number of component carriers, and the numberof aggregated component carriers in the above-mentioned description arecapable of being carried into practice with modifications thereof asappropriate. Further, the invention is capable of being carried intopractice with modifications thereof as appropriate without departingfrom the scope of the invention.

What is claimed is:
 1. Abase station apparatus capable of transmitting adownlink transmission frame at transmission timing different fromanother base station apparatus, the base station apparatus comprising: ablank resource setting section that sets, as a blank resource, aresource corresponding to a downlink control channel included in adownlink transmission frame transmitted from the other base stationapparatus; a user data assigning section that assigns user data to thedownlink transmission frame while avoiding the blank resource; and atransmission section that transmits the downlink transmission frameassigned the user data to a mobile terminal apparatus.
 2. The basestation apparatus according to claim 1, wherein the blank resourcesetting section sets the blank resource based on a shift amount oftransmission timing of the downlink transmission frame with respect tothe downlink transmission frame of the other base station apparatus. 3.The base station apparatus according to claim 2, wherein the blankresource setting section sets the blank resource based on a set positionof a blank period acquired from the other base station apparatus, inaddition to the shift amount.
 4. The base station apparatus according toclaim 1, wherein the blank resource setting section sets, as the blankresource, a resource corresponding to the downlink control channel in asubframe consisting of the downlink control channel and a blank periodin the downlink transmission frame transmitted from the other basestation apparatus.
 5. A mobile terminal apparatus connected to a basestation apparatus capable of transmitting a downlink transmission frameat transmission timing different from another base station apparatus,the mobile terminal apparatus comprising: a blank resource informationacquiring section that acquires blank resource information to identify aresource corresponding to a downlink control channel included in adownlink transmission frame transmitted from the other base stationapparatus, as a blank resource set in the base station apparatus; and auser data demodulation section that demodulates user data received fromthe base station apparatus while avoiding the blank resource, based onthe blank resource information.
 6. The mobile terminal apparatusaccording to claim 5, wherein the blank resource information is a shiftamount of transmission timing of the downlink transmission frame withrespect to the downlink transmission frame from the other base stationapparatus.
 7. A communication control method in a base station apparatuscapable of transmitting a downlink transmission frame at transmissiontiming different from another base station apparatus, the communicationcontrol method comprising: setting, as a blank resource, a resourcecorresponding to a downlink control channel included in a downlinktransmission frame transmitted from the other base station apparatus;assigning user data to the downlink transmission frame while avoidingthe blank resource; and transmitting the downlink transmission frameassigned the user data to a mobile terminal apparatus.